Safety lock for portable lift mechanism

ABSTRACT

A portable lift truck has a vertically movable load receiving carriage which is driven up and down by a power drive mechanism, such as a hydraulic cylinder and chains connecting a cylinder to the lift carriage. In the event of a malfunction of the lift mechanism, such as due to chain breakage or a major hydraulic failure, the lift mechanism is prevented from free falling beyond a predetermined speed. Equally spaced stop lugs on the mast are engaged by an arm on a rotatable stop member which is spring loaded to dump rotation of the stop member when the arm engages the stop lugs. If the relative speed between the stop lugs and the rotatable member substantially exceeds the maximum rate of movement obtainable from the drive mechanism, the spring damping will not react fast enough to prevent an interference lug on the rotatable stop member from jamming into the path of one of the stop lugs, thus locking the lift mechanism against further movement before it achieves any excessive speed.

United States Patent [1 1 Tang [ 1 May 22,1973

[54] SAFETY LOCK FOR PORTABLE LIFT MECHANISM [75] Inventor: AlexanderReuben Tang, Mervue,

Galway, Ireland [73] Assignee: Crown Controls Limited, New

Bremen,Ohio

[22] Filed: Apr. 13, 1972 21 Appl. No.: 243,775

[52] US. Cl ..187/89, 187/9 [51] Int. Cl. ..B66b 5/16 [58] Field ofSearch ..187/9, 38, 89

[56] References Cited UNITED STATES PATENTS 764,038 7/1904 Carpenter..l87/89 3,084,766 4/1963 Donaldson ..187/89 3,276,747 10/1966 Zimmerman..l87/38 Primary ExaminerHarvey C. Homsby Attorney-Lawrence B. Biebel etal.

57 ABSTRACT A portable lift truck has a vertically movable loadreceiving carriage which is driven up and down by a power drivemechanism, such as a hydraulic cylinder and chains connecting a cylinderto the lift carriage. In the event of a malfunction of the liftmechanism, such as due to chain breakage or a major hydraulic failure,the lift mechanism is prevented from free falling beyond a predeterminedspeed. Equally spaced stop lugs on the mast are engaged by an arm on arotatable stop member which is spring loaded to dump rotation of thestop member when the arm engages the stop lugs. If the relative speedbetween the stop lugs and the rotatable member substantially exceeds themaxirnum rate of movement obtainable from the drive mechanism, thespring damping will not react fast enough to prevent an interference lugon the rotatable stop member from jamming into the path of one of thestop lugs, thus locking the lift mechanism against further movementbefore it achieves any excessive speed.

3 Claims, 4 Drawing Figures Patented May 22, 1973 SAFETY LOCK FORPORTABLE LIFT MECHANISM BACKGROUND OF THE INVENTION This inventionrelates to the lift mechanism of portable lift trucks, particularly thekind having a vertically movable power operated lift carriage havingforks or the like for lifting and transporting heavy loads. In theparticular embodiment shown, the type of truck illustrated is one inwhich the operator rides on the vertically movable carriage, however theinvention is not limited to that type of truck.

The usual lift mechanism for the carriage, and in some cases for themoving part of a multi-piece telescopic mast, comprises one or morehydraulic cylinders connected through a chain and sprocket mechanism tothe lift carriage. In the event of a massive hydraulic failure, such asa burst hose, or in the event of breaking of one or more of the chains,if the carriage has a substantial load and is in its raised position, itcan accelerate rapidly and dangerously, dropping or damaging the loadand possibly injuring the operator or other persons in the vicinity.This is especially true if the operator is riding on the carriage in thecase of the so-called stock picker truck. There is a need for someautomatically operable safety mechanis which is simple, sure in itsoperation, and capable of functioning automatically without attention orcareful regular maintenance.

SUMMARY OF THE INVENTION In accordance with the invention the carriageof a lift truck has a rotatable spring loaded stop member mounted on asupporting shaft which is carried on the carriage, and an arm extendsfrom the stop member into a path along one of the parts of the mast.Regularly spaced stop lugs extend from this mast part, thus the arm isin position to strike each of the stop lugs during motion of thecarriage on the mast.

An interfering lug is also provided on the rotatable member, at anangular position such that normally it is withdrawn from the path of thestop lugs. The rotatable motion of the stop member is damped by a springdevice which raises the arm into position behind a stop lug which thearm has engaged, and around which the arm is moving as the carriagerises or lowers at a normal rate. If the motion of the carriage and/orthe lift mechanism substantially exceeds the maximum rate obtainablefrom the drive mechanism, the operation of the spring system is suchthat the unusual acceleration motion of the rotatable stop member willcause the interference lug to swing between the stop lugs and engage thenext one before the stop member can rotate back out of the way. Thislocks the lift mechanism against further movement. During normaloperation of the lift mechanism, the interfering lug is returned out ofthe path of the stop lugs and does not engage them, but the interferenceoccurs automatically if the rate of relative movement between theappropriate lift mechanism parts substantially exceeds the normal rateachieved with the drive mechanism.

The primary object of the invention, therefore, is to provide a novel,simple, and reliable safety device for the lift mechanism of portablelift trucks and the like, as hereinafter described.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view illustrating atypical portable lift truck to which the present invention is applied;

FIG. 2 is a fragmentary view with parts shown in section, illustratingthe novel safety stop mechanism on the carriage of a stock picker typeof lift truck, having a telescopic mast arrangement;

FIG. 3 is a view on the same scale, taken from the right of FIG. 2, withparts broken away to illustrate the safety stop mechanism; and

FIG. 4 is a fragmentary view similar to FIG. 2, but on a slightly largescale, showing the manner in which the rotatable stop member acts toprevent further relative movement of the lift mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, whichillustrates a portable lift truck of the so-called stock picker type,the body of the truck is shown at 10, and includes, for example,suitable storage space for electric storage batteries which providemotive power for a drive motor that in turn is connected to the rearsteering and traction wheel 12. Details of such a drive are well known.Forwardly of the body there are outriggers 14 carrying front supportwheels 50, and a mast structure 18 extends vertically from the frontedge of the body, generally centrally of the truck. In a typicalembodiment, the mast (see FIG. 2) includes stationary channel members20, vertically movable channel members 22 which are guided by rollers 23to run vertically along the stationary channels 20. The carriage 25 ismounted through further rollers 26 to run vertically within the movablechannels 22. The load carrying forks 28 project from the carriage,generally above the outriggers 14 and provide support for loads to belifted and moved.

In the particular embodiment shown, the 'operator stands on a platform30 which is supported as part of the carriage adjacent to the mast, andsuitable controls (not shown) are provided for operation of the truckfrom this position.

The drive mechanism for the lift is typically a hydraulic cylinderlocated between the mast channels, and powered through an electricallydriven hydraulic pump which derives its power from the storagebatteries. Details of these parts are not shown since they areconventional. The hydraulic cylinder is connected through chains or thelike 32 to the carriage 25, and through suitable threading arrangementsof the chain over sprockets, to the telescopic movable mast channels 22(when these are used). Thus, extension and retraction of the hydrauliccylinder produces raising and lowering movement of the carriage 25.

The rate of operation of this lifting device is normally controlled bythe rate of movement of the hydraulic cylinder, but in the event of somebreakage in the drive mechanism connections, such as breaking of one ofthe chains, the carriage could free fall rapidly, particularly if thereis a substantial load on the forks. To prevent this, an automaticallyoperating safety device is provided by the invention.

This device consists of side brackets 35 fastened to the carriage, andhaving a sturdy pivot pin 36 mounted between them. On this pin,preferably carried on a sleeve bushing 37, is a rotatable stop member 40having an arm 42 which extends into a path along one of the channels 22.On this channel there are regularly spaced outwardly extending stop lugs45 which project along the path of the arm 42. Angularly spaced from thearm 42, also extending from the member 40, is an-interfering lug 48which is normally out of the path of the stop lugs 45. A U-shaped guiderod 50 extends around the rotatable stop member 40, being suitablebolted to the bracket, and an ear member 52, fastened to the member 40,slides on the rod 50. Coil springs 54 and 55 surround the rod and engageopposite sides of the ear 52, tending to damp the rotating motion of themember 40 introduced by the arm 42 striking one of the stop lugs 45.

As the carriage lowers relative to the channels 22, the arm 42 willengage one of the lugs 45, and the member 40 will rotate generallyclockwise, with the stop lug passing between the arm 42 and theinterfering lug 48. The spring mechanism returns the swinging orrotating member 40 as soon as the arm 42 clears the stop lug, thuscausing the interfering lug 38 to move away from the path of the stoplugs, and the arm strikes the next lug, etc. This continues so long asthe relative movement between the parts does not exceed that ratenormally achieved by the lift drive mechanism.

However, if the carriage should accelerate due to a lift mechanismfailure, the spring rate of the return spring device is such that itwill not function rapidly enough to withdraw the interfering lug in atimely way, and it will engage the next stop lug 45, the position of theparts being as shown in FIG. 4. The member 40 is held in this positiondue to the fact that stop ears 55, which project as integral extensionsof the member 40, engage a stop surface 57 on the brackets. These stopsprevent further clockwise motion of the member 40 and the interferinglug remains in engagement with the stop lug 45, immediately halting themotion of the carriage.

It will be readily apparent to those skilled in the art that this safetymechanism is of a simple and relatively inexpensive construction, andthat it functions automatically if the carriage achieves a speed inexcess of its normal lowering speed. Obviously, the arrangement of theparts could be reversed or otherwise modified and the stop lugs could beprovided on the stationary mast channels 20 when the telescopic mastmembers 22 are not used.

I claim:

1. In a lift truck having a lift mechanism including a mast with avertically movable power operated carriage for lifting and loweringloads, and a drive mechanism connected to raise and lower the carriage,an improved safety apparatus comprising a series of stop lugs spacedequally by a predetermined amount and a spring loaded stop member withan arm arranged to move into engagement with said stop lugs, said stoplugs and said stop member being mounted on relatively movable parts ofthe lift mechanism such that said arm engages and releases from saidstop lugs in succession during raising and lowering of the mechanism,said stop member also having an interfering lug normally out of the pathof said stop lugs, and a spring device retarding the motion of said stopmember in response to engagement of said arm and said stop lugs wherebythe interfering lug will clear said stop lugs only if the relativemovement between said arm and said stop lugs does not substantiallyexceed the maximum rate of movement attainable from said drivemechanism.

2. Safety apparatus for a lift truck, as defined in claim 1, whereinsaid stop member is rotatably mounted and said arm swings into and outof the path of said stop lugs.

3. Safety apparatus as defined in claim 1 wherein said interfering lugis arranged to jam against a stop lug in response to excessive carriagespeed, and a stop device operates to hold the interfering lug in thejammed position.

1. In a lift truck having a lift mechanism including a mast with avertically movable power operated carriage for lifting and loweringloads, and a drive mechanism connected to raise and lower the carriage,an improved safety apparatus comprising a series of stop lugs spacedequally by a predetermined amount and a spring loaded stop member withan arm arranged to move into engagement with said stop lugs, said stoplugs and said stop member being mounted on relatively movable parts ofthe lift mechanism such that said arm engages and releases from saidstop lugs in succession during raising and lowering of the mechanism,said stop member also having an interfering lug normally out of the pathof said stop lugs, and a spring device retarding the motion of said stopmember in response to engagement of said arm and said stop lugs wherebythe interfering lug will clear said stop lugs only if the relativemovement between said arm and said stop lugs does not substantiallyexceed the maximum rate of movement attainable from said drivemechanism.
 2. Safety apparatus for a lift truck, as defined in claim 1,wherein said stop member is rotatably mounted and said arm swings intoand out of the path of said stop lugs.
 3. Safety apparatus as defined inclaim 1 wherein said interfering lug is arranged to jam against a stoplug in response to excessive carriage speed, and a stop device operatesto hold the interfering lug in the jammed position.